Phase Ib/II study on the safety, tolerability, and preliminary efficacy of pegylated irinotecan (JK1201I) as second‐line monotherapy for patients with small‐cell lung cancer

Abstract Purpose To evaluate the safety, tolerability, and preliminary efficacy of multiple doses of pegylated irinotecan (JK1201I) as a second‐line monotherapy for treating small‐cell lung cancer (SCLC) patients. Methods According to the “3 + 3” dose‐escalation principle, patients received intravenous JK1201I at 180 or 220 mg/m2 once every 3 weeks for four cycles. Progression‐free survival (PFS), overall survival (OS), median progression‐free survival (mPFS), and median overall survival (mOS) were evaluated. The Kaplan–Meier method was used to analyze PFS and overall OS. Brookmeyer and Crowley's method was used for mPFS and mOS. Results This study included 29 patients with stage III–IV SCLC (stage IIIa, n = 1; stage IIIb, n = 1; and stage IV, n = 27). Of these, 26 patients were enrolled in the 180 mg/m2 dose group, and 3 patients were enrolled in the 220 mg/m2 dose group. No dose‐limiting toxicity (DLT) was noted during the first 28 days of treatment. Grade 3 or higher adverse events were recorded in the 180 mg/m2 group, including diarrhea (11.5%, 3/26), neutropenia (7.7%, 2/26), and leukopenia (7.7%, 2/26). In the 220 mg/m2 group, one patient (33.3%, 1/3) experienced neutropenia or leukopenia. In the 180 mg/m2 group, 38.5% (10/26) of patients achieved an objective response rate (ORR), with a disease control rate (DCR) of 73.1% (19/26). The mPFS and mOS were 3.4 and 12.1 months, respectively. In the 220 mg/m2 group, one patient had stable disease, and one had progressive disease (PD). The ORR, DCR, mPFS, and mOS were 0% (0/3) and 33.3% (1/3), 2.7 months and 2.7 months, respectively. Conclusion JK1201I exhibits promising efficacy and relatively low toxicities as a second‐line monotherapy for SCLC, warranting further large‐scale clinical studies to evaluate its efficacy in greater detail.


| INTRODUCTION
Small-cell lung cancer (SCLC) occupies 15%-17% of total lung cancer diagnoses. 1The mOS of SCLC patients is approximately 10 months from the time of diagnosis in 60%-70% of patients with extensive stage (ES) or stage IV SCLC.Chemotherapy and radiotherapy increase survival by 8 months in patients with M1b disease and by 12 months in patients with M1a disease. 2 SCLC is sensitive to platinum-based chemotherapy.These patients underwent platinum-based chemotherapy and reported an ORR of 41.3% (95% confidence interval [CI]: 25.5-59.3)and an mOS of 10.4 months (95% CI: 8.1-14).Thus, topotecan was approved by the US Food and Drug Administration (FDA) and the European Medicines Agency. 3Nevertheless, it is not widely used with hematological toxicities. 4,5urbinectedin was approved by the FDA in June 2020 as second-line chemotherapy for SCLC patients undergoing progression or after platinum-based therapy.In a prospective, single-arm phase II study, Trigo et al. 6 reported an ORR of 35.2% and an OS of 9.3 months with lurbinectedin treatment.In another study, Paz-Ares et al. 7 explored liposomal irinotecan (Onivyde) as a second-line monotherapy in SCLC patients.The primary endpoint was not achieved because the mOS with Onivyde was 7.9 (95% CI: 6.9-9.2) months compared with 8.3 (95% CI: 7.3-9.1)months with topotecan in a phase III study.However, the efficacy of this drug in SCLC appears to be inconsistent.][9] JK1201I is a novel trivalent pegylated irinotecan containing a 20 kDa PEG chain, a biodegradable oligopeptidyl linker, and three irinotecan hydrochloride bonds, demonstrating good tolerability and potential efficacy. 10,11In a phase I trial (NCT04366648), no serious adverse event (SAE) of grade 3 or above was in 19 patients with advanced solid tumors administrated six doses of JK1201I (50, 75, 100, 125, 150, and 180 mg/ m 2 ).A complete response was not found.However, one patient with SCLC in the 150-mg/m 2 dose group exhibited a partial response (PR).Here, we reported the final analysis of the phase II study on the safety, tolerability, and preliminary efficacy of JK1201I as second-line chemotherapy.

| Study design
This present study is a single-arm, open-label, multicenter, phase Ib/II study (Clini calTr ials.gov identifier: NCT05158491).The safety of JK1201I was evaluated in the dose-exploration phase with doses ranging from 180 to 220, 260, and 300 mg/m 2 using a "3 + 3" design.The doseexpansion phase was conducted with 20 patients in each dose group.
Adult SCLC patients aged 18-70 years were included.The patients were enrolled from seven hospitals between December 4, 2021, and October 18, 2022 (Table 1).The inclusion criteria were as follows: (1) an Eastern Cooperative Oncology Group performance status (ECOG-PS) score of 0 or 1; (2) disease progression confirmed by radiology during or after first-line platinumbased chemotherapy for 6 months or less; (3)at least one assessable lesion using the Response Evaluation Criteria in Solid Tumors (RECIST; version 1.1) 12 ; (4) an expected survival time of at least 12 weeks; (5) favorable organ and hematopoietic function and no abnormalities in heart, lung, liver, or kidney function or immune deficiency: White blood cell count of ≥3.5 × 10 9 /L; Absolute neutrophil count (ANC) of ≥1.5 × 10 9 /L; Hemoglobin levels of ≥90 g/L (without recent blood transfusion within 2 weeks); Platelet count of ≥100 × 10 9 /L; Alanine transaminase (ALT) and aspartate aminotransferase (AST) levels within ≤2.5 times the upper limit of normal (ULN), and in cases of liver metastases, AST and ALT levels within ≤5 times the ULN; Serum creatinine concentration within ≤1.5 times the ULN or a creatinine clearance

| Treatment
JK1201I is available as a 40 mg/vial (lyophilized powder; equivalent to irinotecan hydrochloride) and is manufactured by Beijing SL Co., Ltd.(commissioned by JenKem Technology Co., Ltd., Tian Jin; Lot.20,200,902  and 20,210,402).The drug was stored at 2-8°C.The powdered form was diluted in 500 mL of 0.9% sodium chloride solution.Patients received intravenous JK1201I for 240 ± 15 min once every 3 weeks at a dose of 180 or 220 mg/m 2 (as irinotecan hydrochloride) for four cycles.Survival data were collected every 3 months until the last follow-up with the patients or at the end of the study.
Blood samples for pharmacokinetics analysis were collected 60 min before drug administration: 10 min ± 5 min after the start of infusion; 10 min ± 5 min before the end of infusion; and 0 min ± 5 min, 20 min ±5 min, 1 h ± 5 min, 3 h ± 15 min, 6 h ± 30 min, 12 h ± 30 min, 24 h ± 1 h, 48 h ± 2 h, 72 h ± 2 h, 168 h ± 2 h, 240 h ± 2 h, and 336 h ± 4 h after the end of infusion in the first two treatment cycles during the dose-exploration from 4 in the 180-mg/m 2 group and 3 in the 220-mg/m 2 group.
Target lesions were measured at baseline using computed tomography (CT) or magnetic resonance imaging (MRI) within 4 weeks before drug administration.After drug administration, lesions were measured at the end of cycles 2 and 4 or before withdrawal.

| Baseline characteristics
Data on patients' age, sex, height, body weight, body mass index (BMI), ECOG-PS score, tumor stage, time since diagnosis, baseline metastasis, and previous therapies were collected.Table 2 lists the baseline characteristics.The baseline of the lesions was determined based on CT/MRI results obtained within 4 weeks prior to the first administration.Following the initiation of treatment, patients were evaluated using CT/MRI at the end of the second and fourth cycles or prior to withdrawal.

| Assessments and end points
Dose-limiting toxicities (DLTs) were categorized in the initial three patients in both the 180-and 220-mg/m 2 groups during the first 21 days.DLTs were evaluated in four patients in the 180-mg/m 2 group and three in the 220-mg/m 2 group.The AEs 1 : grade 4 neutropenia persisting for at least 3 days or grade 3 febrile neutropenia (ANC of <1000/mm 3 with an oral temperature over 38.3°C measured once or ≥38.0°C lasting 1 h) 2 ; grade 3 thrombocytopenia (25 × 10 9 /L ≤ normal platelet count ≤50 × 10 9 /L) with bleeding, or grade 4 thrombocytopenia with or without bleeding 3 ; any grade 4 hematologic toxicity 4 ; grade 3 or higher non-hematological toxicities excluding hair loss, fatigue, and nausea, vomiting, and diarrhea without maximum supportive therapy.AEs and treatment-emergent AEs (TEAEs) were documented 1 month after the final treatment.Severity was graded using the common terminology criteria for adverse events, version 5.0.
Secondary endpoints encompassed the preliminary efficacy of JK1201I as a second-line monotherapy in SCLC patients and the evaluation of PFS and OS to determine the recommended dose for a phase III study.PFS, as per RECIST (version 1.1), is the duration from the start of chemotherapy to the day of radiographic confirmation of disease progression or death.OS means the period from the commencement of chemotherapy to the date of death from any cause or the last follow-up.
A post hoc supplementary analysis of efficacy outcomes was conducted in the 180-mg/m 2 group, considering factors including age (below or above 65 years), presence or absence of brain/bone/lymphatic metastases at baseline, the interval between the conclusion of firstline treatment and the initial administration of JK1201I (more or less than 3 months), ECOG scores of 0 or 1 before the first administration of JK1201I, receipt or non-receipt of immunotherapy as first-line treatment, exposure time shorter or longer than the median, and the occurrence or non-occurrence of any TEAEs.

| Analysis methods
The Kaplan-Meier (KM) method was employed for PFS and OS.The Brookmeyer and Crowley method was for the mPFS and mOS.The ORR was assessed using the Clopper-Pearson method.Statistical analyses were conducted using SAS software (version 9.4 or higher; Shanghai BioGuider Medical Technology Co., Ltd.).
Sixteen patients (55.2%) received all four cycles of JK1201I treatment, while 13 patients (44.8%) discontinued their treatment cycles: Six showed progressive disease (PD), two withdrew voluntarily, one developed rapid-onset anaphylaxis, one died of pulmonary mucormycosis, one experienced treatment delay for over 2 weeks due to anemia, one developed diarrhea and grade 4 neutropenia with UGT1A1*6 (A/A) homozygosity mutations, and one refused to receive follow-up examinations.All patients were included in the full analysis set (FAS) and safety set (SS), 26 were included in the efficacy analysis set (EAS), seven were included in the pharmacokinetics Abbreviations: AUC 0-∞ , the area under the curve (0-∞); AUC 0-t , the area under the curve (0-t); CI, confidence interval; C max , maximum concentration; SE, standard error.
concentration set (PKCS), and six were included in the pharmacokinetics parameter set (PKPS) and DLT set (DLTS; Table 3).Although DLT was not observed in all dosage settings, dose exploration above 220 mg/m 2 and dose expansion of over 180 mg/m 2 were not performed.
After discussion among the investigators, the dose of 180 mg/m 2 of JK1201I was recommended for the phase III study of SCLC patients.

| Pharmacokinetics analyses
Figure 1 presents plasma concentration-time profiles for JK1201I, free irinotecan, SN-38, and SN-38G.Tables 4-6 detail the primary PK parameters.At 180 and 220 mg/ m 2 doses, most PK parameters in cycles 1 and 2, including maximum concentration (C max ), area under the curve (0-t) (AUC 0-t ), and area under the curve (0-∞) (AUC 0-∞ ), escalated with dose increases.The inclusion of one patient in the 95% CI range of β indicated linear dynamics between doses and PK parameters.We need information with the slightly broad 95% CI range of β (Table 6).Most PK parameters displayed no significant variation between cycles 1 and 2. The half-lives of free irinotecan and SN38 derived from JK1201I were 40.75 and 87.57hours, with C max values of 121.10 and 3.537 ng/mL (Table 4).Compared to data on irinotecan hydrochloride (CPT-11) from Pitot et al., 13 the half-lives of free irinotecan and SN38 were longer at 12.9 and 27.1 h.The respective C max values were >2810 and 41 ng/mL.JK1201I extends the half-lives and tumor exposure of both irinotecan and SN-38, reducing the C max values.The average exposure dose at 180 mg/m 2 was 984.910 ± 433.417 mg, with an average of 48.7 ± 26.39 days (Table 5).

| Preliminary efficacy
Following the revised RECIST guideline (version 1.1), in the 180-mg/m 2 group, PR was achieved in 10 patients, disease was seen in nine, PD was in five, and two were not assessable.The ORR, DCR, mPFS, and mOS were 38.5% (10/26; 95% CI: 20.2-59.4),73.1% (19/26; 95% CI: 52.2-88.4),3.4 months (95% CI: 2.7 months to NA), and 12.1 months (95% CI: 5.9 months to NA).In the 220-mg/ m 2 group, one each exhibited stable disease and PD; the remaining patient was not assessable.The ORR, DCR, and mPFS were 0% (0/3), 33.3% (1/3; 95% CI: 0.8-90.6),and 2.2 months (95% CI: 1.6 months to NA), respectively, while mOS could not be determined (Tables 8 and 9; Figures 2   and 3).Data collection for PFS concluded posttreatment, causing a PFS rate of 0% in the fourth month (Table 10).OS data were updated every 3 months until the electronic data capture system closed on April 11, 2023, with a 16month OS rate of 42.6% in the 180-mg/m 2 group (Table 11).Figures 2 and Figure  (enrolled as #1006).This individual presented with brain and lymphatic metastases but no bone metastases and had an ECOG performance status of 0 at baseline.Immunotherapy was administered as the first-line treatment.The period between the conclusion of the first-line treatment and the initial administration of JK1201I was 6.6 months.The patient completed all four cycles of treatment, with a total exposure time of 67 days, marginally above the median of 63.5 days.The greatest reduction in target lesion size was recorded at −60.2% from the baseline (Figure 4), with the outcomes being PR (Figure 5).The shortest mOS, recorded at 3.58 months, was in a 65-year-old patient (#1004) who had lymphatic metastases but no brain or bone metastases and an ECOG score of 1 at baseline.This patient, receiving immunotherapy as the initial treatment, had 2 months between the end of the first-line treatment and the first dose of JK1201I.Due to disease progression, only two treatment cycles were completed, with the target lesion size change of 56.33% (Figure 4).The mOS of patients experiencing vomiting and patients who did not were 9.9 and 12.1 months.

| DISCUSSION
In our present study, JK1201I exhibited a 6-month OS rate of 75%, a 1-year OS rate of 56.8%, an ORR of 38.5%, and an mOS of 12.1 months in the 180-mg/m 2 group (Tables 8,  9, and 11).These results are also consistent with the meta-analysis performed by Horita et al. involving 1347 patients across 14 articles, 17 which reported 6-month and 1-year OS rates of 37% and 9% in refractory/relapsed patients, and 57% and 27% in sensitive/relapsed patients.Lurbinectedin is approved based on the 6-month and 1year OS rates of 67.1% and 34.2%, an ORR of 35.2%, and an mOS of 9.3 months. 6Patients are not categorized into refractory/relapsed or sensitive/relapsed groups.Based on the dose selection results from the studies above, results suggest that 180 mg/m 2 of JK1201I prolongs the OS of SCLC patients.

| CONCLUSION
The intravenous administration of 180 mg/m 2 of JK1201I once every 3 weeks as a second-line monotherapy exhibited low toxicities.These findings can be further verified by performing a phase III trial comparing F I G U R E 5 Waterfall plot describing best response and corresponding duration.

T A B L E 3
Distribution of patients.

F I G U R E 1
Plasma concentration-time profiles for JK1201I, free irinotecan, SN-38, and SN-38G.
3 depict KM estimates for PFS and OS.Post hoc supplementary analysis results in the 180mg/m 2 group revealed that mOS was longer in patients under 65 years than those over 65 (12.1 vs. 5 months).The maximum OS was 15.01 months in a 45-year-old patient F I G U R E 2 Estimated progressionfree survival (PFS) of patients under different dosages of JK1021I.F I G U R E 3 Estimated overall survival (PFS) of patients under different dosages of JK1021I.LONG et al.

F I G U R E 4
Best change in the target lesion size from baseline (full analysis set).
Hospital list and enrolled number of patients.Demographics and disease characteristics of all patients at baseline (FAS).
T A B L E 1 T A B L E 2Abbreviations: BMI, body mass index; ECOG-PS, Eastern Cooperative Oncology Group performance status; FAS, full analysis set; SCLC, small-cell lung
T A B L E 4a Time relative to the start of the infusion.Abbreviations: AUC 0-∞ , the area under the curve (0-∞); AUC 0-t , the area under the curve (0-t); C max , maximum concentration; T max , time to maximum concentration;T A B L E 5 T A B L E 6 Overview of TEAEs (safety set).
T A B L E 7Abbreviations: SAE, serious adverse event; TEAE, Treatment-Emergent Adverse Event; TRAE, treatment-related adverse event;T A B L E 8 Outcomes of antitumor activity (FAS).Abbreviations: EAS, efficacy analysis set; OS, overall survival; PD, progressive disease;